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Communications, IEEE Transactions on

Issue 6 • Date Jun 1998

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Displaying Results 1 - 18 of 18
  • The performance of a link with multipriority traffic

    Publication Year: 1998 , Page(s): 743 - 746
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    This letter discusses the performance of a link carrying calls of preemptive priorities. General κ-dimensional steady-state balance equations are deduced and the computational complexity of two solution methods are compared through an example of three priorities. The performance of the link is studied through two conventional metrics for blocking probabilities and preempting probabilities. The “peaking” phenomenon of the preempting line discussed can be used in the design of switches and networks. The coincidence of the preempting probability line with the blocking probability line, displayed in the discussion of numerical results, suggests that better metrics for preemptive performance must be found View full abstract»

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  • A novel digital lock detector for QPSK receiver

    Publication Year: 1998 , Page(s): 750 - 753
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A new lock detection algorithm for digital quadrature phase-shift keying (QPSK) receiver is proposed. Analysis of the detector's output characteristics is given and is verified by using computer simulation. Performance degradation due to carrier jitter is also considered. Analytic and simulation results show that the proposed algorithm is very useful as a lock detector in digital receivers because it has a good detection performance and simple structure View full abstract»

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  • An efficient code-timing estimator for receiver diversity DS-CDMA systems

    Publication Year: 1998 , Page(s): 826 - 835
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    We propose an efficient algorithm for estimating the code timing of direct-sequence code-division multiple-access (DS-CDMA) systems that consist of an arbitrary antenna array at the receiver and work in a flat-fading and near-far environment. The algorithm is an asymptotic (for large number of data samples) maximum-likelihood (ML) estimator that is derived by modeling the known training sequence as the desired signal and all other signals including the interfering signals and the additive noise as unknown colored Gaussian noise. The algorithm does not require the search over a parameter space and the code timing is obtained by rooting a second-order polynomial, which is computationally very efficient. Simulation results show that the algorithm is quite robust against the near-far problem and channel fading. It requires a shorter training sequence than the single-antenna-based estimators View full abstract»

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  • An efficient algorithm for estimating the signal-to-interference ratio in TDMA cellular systems

    Publication Year: 1998 , Page(s): 728 - 731
    Cited by:  Papers (33)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    A new algorithm is proposed for estimating the signal-to-interference plus noise ratio S/(I+N) in time-division multiple-access (TDMA) cellular systems. The S/(I+N) estimator is evaluated for use in the IS-54/136 system and a GSM-like system, and compared with existing techniques. The algorithm has a mean square prediction error that is comparable to the best known S/(I+N) estimation schemes, but with a significantly reduced computational complexity View full abstract»

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  • ECI value generations in CSE-based distributors

    Publication Year: 1998 , Page(s): 738 - 742
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    In this letter we consider two efficient external control input (ECI) value generation methods for the controlled switching element (CSE)-based distributor, which is a new distributor structure that does not require the dummy address generation and extraction operations of the conventional distributors. The first method relies on the active packet counter and the ECI generator for ECI value generation, and the second method utilizes the intrinsic ECI generation property of the CSE-based reverse banyan network (RBN). The first method brings forth a flexible distributor structure, while the second method renders a very simple structure. In fact, the second method yields the so-called autonomous distributor, consisting only of a CSE-based RBN and a set of delays, which is perceived as the simplest among all available distributors. In addition, we introduce a modified version of the autonomous distributor which can speed up the connection-state setup process View full abstract»

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  • Radio resource allocation in fixed broadband wireless networks

    Publication Year: 1998 , Page(s): 806 - 818
    Cited by:  Papers (24)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    We consider use of fixed broadband wireless networks to provide packet services for telecommuting and Internet access. Each cell is divided into multiple sectors, each of them served by a sector antenna colocated with the base station (BS), and user terminals also use directional antennas mounted on the rooftops of homes or small offices and pointed to their respective BS antennas. To support a target data rate of 10 Mb/s, a bandwidth of several MHz is required. Since radio spectrum is expensive, the bandwidth needs to be reused very aggressively. Thus, efficient strategies for frequency reuse and managing cochannel interference are critically important. We propose several algorithms for dynamic radio-resource allocation in the fixed wireless networks. In particular, a method to be referred to as the staggered resource allocation (SRA) method uses a distributed scheduling algorithm to avoid major sources of interference while allowing concurrent packet transmission and meeting signal-to-interference objectives. The performance of the method is studied by analytic approximations and detailed simulation. Our results show that the combination of directional antennas plus the SRA method is highly effective in controlling cochannel interference. For reasonable system parameters, the SRA method delivers a throughput in excess of 30% per sector while permitting a given frequency band to be reused in every sector of every cell. It also provides satisfactory probability of successful packet transmission. In addition, a simple control mechanism can be applied in the method to improve performance for harsh radio environments View full abstract»

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  • A simple decoding of BCH codes over GF(2m)

    Publication Year: 1998 , Page(s): 709 - 716
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    A simple decoding method for even minimum-distance Bose-Chaudhuri-Hochquenghem (BCH) codes is proposed. In the method the coefficients of an error locator polynomial are given as simple determinants (named Q determinants) composed of syndromes. The error evaluator is realized as a Q determinant divided by an error locator polynomial. The Q determinants can be efficiently obtained with very simple calculations on syndromes enabling the realization of a high-speed decoder of simple configuration. The number of calculations in obtaining the error locator and the error evaluator with the proposed method is smaller than that with the widely used Berlekamp-Massey algorithm when the number of correctable errors of the code is five or less. The proposed method can also be applied to the binary narrow-sense BCH codes of odd minimum distance View full abstract»

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  • On the windowed Cholesky factorization of the time-varying asynchronous CDMA channel

    Publication Year: 1998 , Page(s): 735 - 737
    Cited by:  Papers (13)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    In this letter we present a simplified proof for the convergence of the windowed Cholesky factorization of the time-varying asynchronous code-division multiple-access (CDMA) channel View full abstract»

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  • Error probabilities for QAM systems on partially coherent channels with intersymbol interference and crosstalk

    Publication Year: 1998 , Page(s): 775 - 783
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    We describe an efficient procedure to calculate the probability of error Pe for a quadrature amplitude modulation (QAM) communications system operating over a channel that introduces distortion, interference, and noise. The method is an extension of the saddlepoint integration technique introduced by Helstrom (1986) to efficiently evaluate Pe for one-dimensional pulse-amplitude modulation (PAM) systems with intersymbol interference (ISI) and crosstalk. We consider the effects of noise, random carrier phase offset, ISI, and crosstalk between the I and Q channels. The error probability is written as a double Laplace inversion integral and can be easily applied to any rectangular constellation. This integral is calculated by extending the saddlepoint integration technique to two complex dimensions. Results are presented for QAM systems with 16, 64, and 256 symbols. The technique can be directly extended to environments with cochannel interference consisting of other QAM signals View full abstract»

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  • Periodic timing error components in feedback synchronizers operating on nonsynchronized signal samples

    Publication Year: 1998 , Page(s): 747 - 749
    Cited by:  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB)  

    This letter shows that the synchronization error resulting from a timing recovery loop, operating on nonsynchronized samples of a noisy sinusoid, contains periodic components. This periodic timing jitter is caused solely by nonideal interpolation between the nonsynchronized signal samples and is absent when using synchronized sampling. The results of our linearized tracking analysis are confirmed by computer simulations View full abstract»

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  • A novel approach for reduction of blocking effects in low-bit-rate image compression

    Publication Year: 1998 , Page(s): 732 - 734
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB)  

    In this letter we propose a new approach for removing blocking artifacts in reconstructed block-encoded images. The key of the approach is using piecewise similarity within different parts of the image as a priori to give reasonable modifications to the block boundary pixels. This makes our approach different from traditional ones, which are often developed by applying some kinds of smoothing constraints on local regions. Experimental results show that our approach well achieves enhanced decoding for JPEG-decoded images both objectively and subjectively View full abstract»

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  • New performance bounds for turbo codes

    Publication Year: 1998 , Page(s): 717 - 723
    Cited by:  Papers (53)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    We derive a new upper bound on the word- and bit-error probabilities of turbo codes with maximum-likelihood decoding by using the Gallager bound. Since the derivation of the bound for a given interleaver is intractable, we assume uniform interleaving as in the derivation of the standard union bound for turbo codes. The result is a generalization of the transfer function bound and remains useful for a wider range of signal-to-noise ratios, particularly for some range below the channel cutoff rate. The new bound is also applicable to other linear codes View full abstract»

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  • Waveform analysis of jitter in SRTS using continued fraction

    Publication Year: 1998 , Page(s): 819 - 825
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    This paper presents a method to analyze jitter waveform in synchronous residual time stamp (SRTS) using continued fraction. It is shown first that the jitter waveform can be decomposed into triangular wave components and that each component corresponds to a rational approximation value of a parameter called residue. Next, quasi-simple continued fraction expansion of the residue is defined to obtain rational approximation values of the residue in a systematic manner. This method gives a series of rational approximation values of the residue. It corresponds to the decomposition of the SRTS jitter waveform into triangular wave components. Many characteristics of the jitter waveform are derived by the quasi-simple continued fraction expansion of the residue. Especially, the average amplitude and period of each triangular wave component are given View full abstract»

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  • Two-dimensional low-pass filtering codes

    Publication Year: 1998 , Page(s): 724 - 727
    Cited by:  Papers (19)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    We describe a framework for designing encoders that transform arbitrary data sequences into two-dimensional arrays satisfying certain constraints, in particular, constraints that guarantee arrays with limited high spatial frequency content. We also exhibit specific codes that produce such arrays. Such codes are useful for holographic recording systems View full abstract»

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  • List decoding of turbo codes

    Publication Year: 1998 , Page(s): 754 - 762
    Cited by:  Papers (21)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    List decoding of turbo codes is analyzed under the assumption of a maximum-likelihood (ML) list decoder. It is shown that large asymptotic gains can be achieved on both the additive white Gaussian noise (AWGN) and fully interleaved flat Rayleigh-fading channels. It is also shown that the relative asymptotic gains for turbo codes are larger than those for convolutional codes. Finally, a practical list decoding algorithm based on the list output Viterbi algorithm (LOVA) is proposed as an approximation to the ML list decoder. Simulation results show that the proposed algorithm provides significant gains corroborating the analytical results. The asymptotic gain manifests itself as a reduction in the bit-error rate (BER) and frame-error rate (FER) floor of turbo codes View full abstract»

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  • Cochannel interference reduction in optical PPM-CDMA systems

    Publication Year: 1998 , Page(s): 799 - 805
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    A multiple-user interference reduction technique is proposed for optical code-division multiple-access (CDMA) systems. Data symbols from each user are encoded using a pulse-position modulation (PPM) scheme before multiplexing. Modified prime sequences are adopted as the signature codes in the multiplexing process. An interesting property of this code is the uniformity of the cross correlation among its sequences. This property is the main key in constructing the multiple-access interference canceler. In addition to its simplicity, this canceler offers a great improvement in the error probability as compared to the system without cancellation. A simple modification to this canceler that enhances its performance is proposed as well View full abstract»

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  • Stochastic power control for cellular radio systems

    Publication Year: 1998 , Page(s): 784 - 798
    Cited by:  Papers (124)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    For wireless communication systems, iterative power control algorithms have been proposed to minimize the transmitter power while maintaining reliable communication between mobiles and base stations. To derive deterministic convergence results, these algorithms require perfect measurements of one or more of the following parameters: (1) the mobile's signal-to-interference ratio (SIR) at the receiver; (2) the interference experienced by the mobile; and (3) the bit-error rate. However, these quantities are often difficult to measure and deterministic convergence results neglect the effect of stochastic measurements. We develop distributed iterative power control algorithms that use readily available measurements. Two classes of power control algorithms are proposed. Since the measurements are random, the proposed algorithms evolve stochastically and we define the convergence in terms of the mean-squared error (MSE) of the power vector from the optimal power vector that is the solution of a feasible deterministic power control problem. For the first class of power control algorithms using fixed step size sequences, we obtain finite lower and upper bounds for the MSE by appropriate selection of the step size. We also show that these bounds go to zero, implying convergence in the MSE sense, as the step size goes to zero. For the second class of power control algorithms, which are based on the stochastic approximations method and use time-varying step size sequences, we prove that the MSE goes to zero. Both classes of algorithms are distributed in the sense that each user needs only to know its own channel gain to its assigned base station and its own matched filter output at its assigned base station to update its power View full abstract»

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  • An equalizer design technique for the PCM modem: a new modem for the digital public switched network

    Publication Year: 1998 , Page(s): 763 - 774
    Cited by:  Papers (12)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Modems designed for the public switched telephone network (PSTN) have conventionally been based on modeling assumptions which view the PSTN connection as an essentially analog medium. However, as the PSTN evolves toward all digital transport and switching, and particularly as major traffic sources, such as Internet service providers, increasingly have direct digital connections to the PSTN, it is appropriate to revisit the model assumptions. Recently, several modem and chipset manufacturers have announced “56 K” modems based on an emerging system paradigm in which one user (a residential Internet subscriber) has an analog connection to the PSTN, and the other (an Internet service provider) has a digital one. ITU-T is expected to finalize details of a corresponding recommendation in 1998. With this configuration, modem designs based on signaling with the μ-law alphabet become feasible, and the conventional Shannon limit disappears as the quantization noise is avoided. Thus, the conventional Shannon limit of about 36 kb/s can be beaten, and it is possible to approach the digital transmission rate of 64 kb/s. Modems employing this general approach have become known as μ-law or pulse-code modulation (PCM) modems. In this paper we present a signaling technique and the sampling theory based on this technique, display the structure and operating principles of a PCM modem equalizer, and show how this equalizer problem can be cast in the language of multiinput-multioutput (MIMO) system theory View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia